Contemporary hard disk drives include an actuator assembly pivoting through an actuator pivot to position one or more read-write heads, embedded in sliders, each over a rotating disk surface. The data stored on the rotating disk surface is typically arranged in concentric tracks. To access the data of a track, a servo controller first positions the read-write head by electrically stimulating the voice coil motor, which couples through the voice coil and an actuator arm to move a head gimbal assembly in lateral positioning the slider close to the track. Once the read-write head is close to the track, the servo controller typically enters an operational mode known herein as track following. It is during track following mode that the read-write head is used to access the data stored of the track.
Micro-actuators provide a second actuation stage for lateral positioning the read-write head during track following mode. They often use an electrostatic effect and/or a piezoelectric effect to rapidly make fine position changes. They have doubled the bandwidth of servo controllers and are believed essential for high capacity hard disk drives from hereon.
A central feature of the hard disk drive industry is its quest for greater data storage density, leading to continued reduction in track width, the flying height or vertical positioning of the read-write head off the rotating disk surface, and the size of the read head within the read-write head. As these factor shrink, the possibility of the read-write head contacting the rotating disk surface increases and the potential for damage to the disk surface and the
There are a number of proposals and experimental devices pointing to mounting a vertical micro-actuator either directly coupled to the slider parallel the air bearing surface and often employing a piezoelectric effect to induce a strain on the slider to alter the vertical position of the read-write head above the rotating disk surface. These proposals have tended to be ineffective. Another alternative uses a heating element the vertical micro-actuator 98 embedded in a slider 90 to expand the slider distortion zone 97 and reduce the vertical distance Vp between the slider and a rotating disk surface 120-1 from an initial vertical distance Vp0 to a reduced vertical distance Vp1 as shown in FIG. 1A. While this approach is gaining favor at this time it has a significant limitation, it can only actively move the read-write head 94 closer to the rotating disk surface. There are situations where the read-write head needs to be further away from the rotating disk surface, and in those situations this approach does not help. What is needed is a vertical micro-actuator which can both actively lower and raise the read-write head.